In one type of processing system the crop travels axially parallel to and helically around the rotational axis of one or more rotary processing devices commonly referred to as rotors. In other systems, during at least a portion of its travel through the system the crop travels in a transverse or tangential direction relative to the rotational axis of a rotary processing device commonly referred to as a threshing cylinder. In each case, grain is processed between elements affixed to the periphery of the rotary device and arcuate, usually foraminous, stationary processing members in the form of threshing concaves or separating grates that partially wrap around the lower portion of the device.
Because processing systems are utilized to harvest a wide variety of different crops and must function properly in many different operating conditions, it is important to be able to conveniently and accurately adjust the running clearance in the region between the rotary processing devices and stationary processing members to best accommodate these variables. However, it is also important to provide a way of suitably changing the cross-sectional shape of such regions as the running clearance is adjusted whereby to assure that proper processing action is obtained throughout the range of adjustment. While systems using axial flow have somewhat different specific requirements from system using transverse flow due to their different principles of operation, they can both benefit from an ability to appropriately adjust the cross-sectional shape of their processing regions as the running clearance is increased or decreased.